1. Field of the Invention
The present invention relates to a modulator which replaces a part of main information with specific information.
2. Description of the Related Art
In some cases, confidential information that is not intended for disclosure to users is recorded on a recording medium such as a CD (Compact Disk), a DVD (Digital Versatile Disk), and the like. For example, when various contents such as images, sounds, texts, and the like are encoded and recorded onto the recording medium, the encoded contents and an encryption key for decoding the contents as confidential information are recorded. This enables both reproduction of the contents and prevention of illegal copy thereof to thereby protect a copyrighted work contained in the contents.
Note that a technique of modulating a cryptographic key by a modulator different from a modulator for an information data block and recording it onto a recording medium is disclosed (see Japanese Patent Laid-open Application No. 2003-109302). Besides, a technique of converting first information K1 containing a component for decoding contents and second information containing a component for decoding the first information by conversion rules φ1 and φ2 respectively and recording them onto a recording medium is disclosed (see Japanese Patent Laid-open Application No. 2003-122637).